A tool changer according to this invention is structured to be secured to existing vertical milling machines. Vertical milling machines have a horizontal table upon which the workpiece is fastened. The table may be automatically adjusted in two horizontal directions simultaneously. The directions of movement are often referred to as the x and y axes. The milling machine has a spindle into which tool holders may be secured. (As is well known to machinists, tools such as drills, routers, and the like are integrally secured to the tool holders. Thus changing tool holders means changing tools.) The spindle is driven in rotation to turn the tool holder and to cut the workpiece. The spindle is vertically adjustable from an upwardmost position to enable the tool to engage the workpiece. The direction of spindle movement is often referred to as the z axis. The upwardmost position of the spindle is the position in which the tool holder can be secured or released in the spindle. Thus, the upwardmost position of the spindle is referred to as the tool change position.
Spindles and tool holders are standardized throughout the industry. The tool changer specifically described herein is useful with type 30 and type 40 tool holders. These have an upper cylindrical shank with a threaded bore therein. A drawbar (part of the spindle) turns into the threaded bore to draw a conical portion of the tool holder into a conical seat in the spindle. The tool holder must be held up into the spindle for the drawbar to engage it. The tool holder must also be supported when the drawbar releases it. Because, the tool holder is not supported against rotation when being secured or released, the drawbar is typically driven by an impact wrench. What has been described so far with regard to tool holders and milling machines is part of the prior art with which the tool changer according to this invention may be associated.
Machining centers are systems for machining a workpiece requiring, at most, the manual placement of the workpiece upon the machine and the manual removal of the workpiece upon completion. All tool selection, workpiece positioning, and spindle speed adjustments are made automatically either under a punched tape numerical control or a more modern computer numerical control (CNC). Some machining centers are designed from ground up. However, there exists a large capital investment in manually operated or simple numerical controlled milling machines with manual tool changing. Many of these existing milling machines can be upgraded to machining center capability by the further addition of a tool changer. The tool designs that have been proposed, and in some cases actually commercialized, have had drawbacks. Prior add-on tool changers are illustrated, for example, in U.S. Pat. Nos. 3,949,462; 3,951,273; 3,955,267; and 3,872,743. For a tool changer designed to be added to existing milling machines to be practical, it must be simple, rugged, reliable, fast and have a minimum of expensive parts. Moreover, since there are a large number of models of milling machines each having a different configuration available for retrofitting, a tool changer must be easily adapted to each without redesign of complicated parts. Most important, the tool changer must not reduce the capabilities of the milling machine upon which it is mounted by physically interfering with the existing motion.
It is an advantage according to this invention to provide a tool changer adaptable to existing milling machines to upgrade them to machining center capability.
It is an advantage according to this invention to provide a tool changer easily adaptable to a large variety of milling machines by the simple substitution of brackets between the milling machine and the tool changer and/or brackets between the tool store and the tool changing arm.
It is an advantage according to this invention to reduce the complexity of the tool changing and storing mechanism by making unique use of microprocessor technology.
It is an advantage according to this invention to facilitate integration with existing numerical and computer numerical control systems by making unique use of microprocessor technology to enable all tool changer functions including spindle, brake and drawbar functions to issue in reponse to a single command from the numerical control.
It is an advantage according to this invention to provide for rapid tool changing by unique use of microprocessor technology to eliminate or substantially entirely eliminate waiting for tool holders within the tool store to be presented to the tool changing arm.
It is an advantage according to this invention that the next tool holder needed can be advanced to the ready position while the preceding tool is being used and no movement of hangers within the tool store is required thereafter until exchange of tool holders is complete.
It is a further advantage that tool hangers within the tool store can be moved by a substantially continuous motion through the shortest distance by the unique use of servodrive technology. There is no need for each tool holder to come to rest as it passes the ready position. It permits the tool hangers to be located precisely at the ready position without the need to activate additional yoke, pin or stop mechanisms.
It is a further advantage that under most modes of operation, there exists no need to drive the tool carousel and twin claw exchange are simultaneously thus eliminating the potential for clashing.
It is a further advantage according to this invention that the tool holders always remain tool down, whether in the spindle, in the tool store or therebetween, thus improving cleanliness of the tools and eliminating the need for wrist action in the twin claw transfer arm.
It is a further advantage according to this invention to provide a mechanism for engaging the tool holders in the tool store hangers which requires only a small modification of existing tool holders in a location that in no way interferes with the functioning of the tool holder when in the spindle.